The present invention relates to industrial filtration apparatus and, more particularly, to a rotary drum filter utilizing a cloth type media.
One method of filtering solids suspended in a liquid is to submerge a rotary drum filter in a tank of liquid to be filtered. A pressure differential is established between the inner portion of the drum filter and the liquid to be filtered such that the liquid to be filtered is drawn into the drum filter through the appropriately perforated walls of the drum filter. A major problem with such filters is the type of filter media selected to be used on the outer walls of the drum filter. It is most desirable to use a cloth type, also called a permanent media type, filter media on the outer wall of the drum filter as the type of cloth selected can give the desired filter performance characteristics. Such characteristics include flow rate and the degree of suspended solid or fines removal. However, it has proven extremely difficult to remove such fines from the filter media. In many cases it has been necessary to shut down the filtering operation and perform the necessary scraping and removal of the accumulated solids from the outer surface of the filter media. This is undesirable as such down time introduces an equivalent down time in the manufacturing operation to which the industrial filter is connected.
Accordingly, it is an object of the present invention to provide a rotary drum filter capable of continuous filtering operation and further capable of removal of accumulated solids on the filter media during such filtering operation.
The present invention utilizes a rotary drum filter and, in a preferred embodiment, two rotary drum filters, suspended in a tank containing liquid to be filtered. Most typically these rotary drum filters are vertically mounted in the tank, but with appropriate sealing, the rotary drum filters could be mounted horizontally or at other required angles in the tank.
A suction pipe is located within the rotary drum mechanism and is coaxial therewith. Further, the drum is actually connected to the suction pipe through a rotary bearing and seal configuration. This bearing supports the weight of the drum and provides resistance against side thrust from the drive mechanism used to rotate the drum. In the preferred two rotating drum arrangement, each drum is rotated about its center line axis by a single drive mechanism operatively connected to each drum. The drive can be either an air cylinder and ratchet combination or an electric motor and reducer combination. The drive rotates a shaft on which is mounted a sprocket that meshes with chains wrapped around and attached to the upper end of each drum.
The drums are rotated for the purpose of removing the accumulated solids or cake from the outer surface of the filter media. A backwash vacuum box or suction box comprising a generally elongated rectangular arrangement is provided in contact with the filter media of the single drum or with both drums in the preferred two rotary drum arrangement. As the drums are rotated at about one revolution per minute past the vacuum box which covers only a small portion of the entire circumference of the drum, a partial vacuum is drawn in the vacuum box such that filtered liquid is drawn from the inside of the rotary drum through the filter media into the vacuum box. Accordingly, the accumulated solid cake on the outer surface of the media is removed and discharged to the vacuum box. Filtration through the filter media not in contact with the vacuum box continues during such backwashing operation. Depending on the flow rate and filter media chosen, the degree of vacuum drawn through the suction pipe and established within the rotary drum filter is about eight-ten inches of mercury (20-25 cm.). The partial vacuum established in the vacuum box is at about twelve-fifteen inches of mercury (30-38 cm.). Accordingly, a pressure differential exists between the filtered liquid in the rotary drum filter and in the vacuum box when a vacuum is drawn in the vacuum box. Filtered liquid will flow from the rotary drum filter through the portion of the filter media adjacent the vacuum box. This action causes the accumulated solids or cake built up on the filter media to be broken away and deposited in the vacuum box. Appropriate sludge accumulation equipment is part of the vacuum box arrangement for disposal of the filtered cake. Sealing flaps of a rubber like material can also be provided on the edges of the vacuum box adjacent and in contact with the filter media. Such flaps aid in the separation of heavier caking of filtered solids away from the filter media. Such solids would fall to the bottom of the tank wherein appropriate conveyor equipment would carry such solids away for proper disposal. The vacuum box would be actuated by various means such as sensing devices to detect a particular rise in vacuum between the rotary drum filter and the liquid to be filtered in the tank, by a timer setting or by simple manual actuation. It is important to realize that the filtration accomplished by the rotary drum filters can continue during the actuation of the rotation mechanism and the vacuum box. It may be necessary, for example, to actuate the rotation device and vacuum box for only one or two times per hour of filtration. Further, filtration continues to take place during the activation of the vacuum box. Once the rotary drum filter has accomplished one complete revolution, adequate removal of the filter cake from the filter media occurs such that the vacuum box and rotation mechanism may be deactivated until further build up of solids on the filter media has occurred. It should also be noted that the filter media is appropriately joined at the top and bottom of the rotary drum by such means as rubber O rings which hold the filter media embedded in a groove at the top and at the bottom of the rotary drum .